Electronic image composition systems are known, having storage means for storing video signals representing at least two pictures, preview means for displaying a series of artist-selected transformations of a first of said pictures, or a part thereof, until a desired transformation is perceived, and compositing means for thereafter producing composite pictures by combining transformed video signals, or a part thereof, with video signals of a second of said pictures.
An example of such a system is that included in the video graphic equipment manufactured by the present Assignee/Applicant and sold under the trade mark "PAINTBOX". In addition to the composition system, this equipment also includes an electronic painting system which allows an artist to "paint" either or both of said pictures into the storage means, in response to (among other things) movement of a stylus over a touch tablet, which simulates a painting or drawing implement. The image composition system referred to above is described in U.S. Pat. No. 4,602,286 and equivalent British Patent No. 2113950 and the associated painting system is described in greater detail in U.S.. Pat. No. 4,514,818 and equivalent British Patent No. 2089625 both assigned to the present Assignee and included herein as part of the present disclosure.
In the equipment manufactured by the present Assignee and sold under the trade mark "PAINTBOX", additional storage means are provided which allow the painting system to create a control image which may be used to simulate a stencil, whereby part of the image being composed may be masked while the remainder remains exposed for further modification. This stencil signal is also used during operation of the compositing means to control the combining of video signals so as to simulate the "pasting" of the (transformed) chosen part of the first picture into the second picture. The preview means allows an artist to effect a series of transformations to the first picture (which may include changes in size, position, perspective orientation) until a desired transformation is perceived, whereupon (in response to a "stick" command) the compositing means combines the two images into a single store. The type of transformation required is defined by using predetermined movements of the stylus upon the touch tablet which is then implemented by reading video signals from the storage means in a different order from that in which they were written to said storage means.
To assist an artist in effecting the desired transformation, it is desirable for the transformed pictures to be displayed in real-time during preview that is to say, any operation effected by the artist should be displayed substantially instantaneously. However, the calculations involved in many of the transformations are not trivial and have to be repeated for each pixel in the transformed output. Thus, in practice, a portion of an image (often referred to as a "cut-out") can only be transformed in real-time if restrictions are placed on the number of pixels making up the cut-out or, alternatively, if the cut-out is shown as a surrounding margin which is manipulated in real-time, whereafter the full image is processed once the desired position has been identified by manipulation of the margin.